Method for regulating the speed of an internal combustion engine

ABSTRACT

A method for regulating the speed of an internal combustion engine. According to the invention, a second regulation difference (dR 2 ) is calculated by a second filter in the event of dynamic changes of state. In this way, in the event of dynamic changes of state, a speed regulator defines a power-determining signal (ve) according to a first regulation difference (dR 1 ) and the second regulation difference (dR 2 ). The inventive method thus increases the dynamics of the control loop.

PRIORITY CLAIM

This is a 35 U.S.C. §371 National Stage of International Application No.PCT/EP2003/012786, filed on Nov. 15, 2003. Priority is claimed on thatapplication and on the following application:

Country: Germany, Application No. 102 53 739.9, Filed: Nov. 19, 2002.

BACKGROUND OF THE INVENTION

The invention concerns a method for the closed-loop speed control of aninternal combustion engine.

The speed of a drive unit is typically automatically controlled to anidling speed and a final speed. A drive unit is understood to meaneither an internal combustion engine-transmission unit or an internalcombustion engine-generator unit. To achieve closed-loop speed control,the speed of the crankshaft is detected as a controlled value andcompared with an engine speed set value, i.e., the reference input. Theresulting control deviation is converted by a speed controller to acorrecting variable for the internal combustion engine, for example, aninjection quantity. The problem with a control loop of this type is thattorsional oscillations, which are superimposed on the controlled value,can be amplified by the speed controller. This can lead to instabilityof the closed-loop control system

The problem of instability is countered by a speed filter in thefeedback path of the closed-loop speed control system. EP 0 059 585 B1describes a speed filter of this type, in which the timing values of ashaft teeth are detected by means of an operating cycle of the internalcombustion engine. The operating cycle is defined as two revolutions ofthe crankshaft, corresponding to 720°. These tooth timing values arethen used to calculate a filtered tooth timing value by taking thearithmetic mean. This filtered tooth timing value corresponds to thefiltered actual speed value, which is then used for the automaticcontrol of the internal combustion engine.

A closed-loop speed control system for automatically controlling a driveunit with a speed filter of this type in the feedback path is described,for example, in DE 199 53 767 C2.

However, the problem with this two-revolution filter in the feedbackpath is that stable behavior of the drive unit is accompanied bydeterioration of the design load behavior.

SUMMARY OF THE INVENTION

The goal of the invention is to optimize the closed-loop speed controlsystem with respect to design load behavior.

In accordance with the invention, a second filter is used to compute asecond filtered actual speed from the actual speed of the internalcombustion engine, and then a second control deviation is computed fromthis second filtered actual speed. In the event of a dynamic change ofstate, the speed controller computes a power-determining signal, forexample, an injection quantity, from the first and second controldeviations. In this regard, the power-determining signal in the event ofa dynamic change of state is substantially determined from the secondcontrol deviation.

A dynamic change of state occurs when a large deviation between set andactual speed values is present, for example, when a load application orload rejection occurs. The second filter is realized, e.g., as a meanvalue filter with a filter angle of 90°, for fast detection of thisdynamic event. Compared to the two-revolution filter, a filtered speedvalue is present at a significantly earlier point in time, i.e., thedynamic change of state is detected faster.

The invention offers the advantage that couplings with a low naturalfrequency can be used. Since the second filter constitutes a puresoftware solution, it can be subsequently integrated in already existingengine control software.

When a dynamic change of state occurs, the second control deviation actson a proportional component (P component) or a DT1 component of thespeed controller. Suitable characteristic curves are provided for thispurpose.

Preferred embodiments of the invention are illustrated in the drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a system diagram;

FIG. 2 shows a closed-loop speed control system;

FIG. 3 shows a functional block diagram of the speed controller;

FIG. 4 shows a characteristic curve;

FIG. 5 shows a functional block diagram of the speed controller (secondembodiment); and

FIG. 6 shows a characteristic curve.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a system diagram of the overall system of a drive unit 1,for example, an internal combustion engine-generator unit. It comprisesan internal combustion engine 2 with an engine load 4. The internalcombustion engine 2 drives the engine load 4 via a shaft with atransmission element 3. In the illustrated internal combustion engine 2,the fuel is injected by a common-rail injection system. This injectionsystem comprises the following components: pumps 7 with a suctionthrottle for conveying the fuel from a fuel tank 6; a rail 8 for storingthe fuel; and injectors 10 for injecting the fuel from the rail 8 intothe combustion chambers of the internal combustion engine 2.

The internal combustion engine 2 is automatically controlled by theelectronic control unit (EDC) 5. The electronic control unit 5 containsthe usual components of a microcomputer system, for example, amicroprocessor, interface adapters, buffers, and memory components(EEPROM, RAM). The relevant operating characteristics for the operationof the internal combustion engine 2 are applied in the memory componentsin input-output maps/characteristic curves. The electronic control unit5 uses these to compute the output variables from the input variables.FIG. 1 shows the following input variables as examples: a rail pressurepCR, which is measured by means of a rail pressure sensor 9; an actualspeed nM(IST) of the internal combustion engine 2; an input variable E;and a signal FP for the power presetting by the operator. In a motorvehicle application, this corresponds to the position of the acceleratorpedal. Examples of input variables E are the charge air pressure of theturbochargers and the temperatures of the coolant/lubricant and thefuel.

As output variables of the electronic control unit 5, FIG. 1 shows asignal ADV for controlling the pumps 7 with a suction throttle and anoutput variable A. The output variable A is representative of the othercontrol signals for automatically controlling the internal combustionengine 2, for example, the injection start SB and a power-determiningsignal ve, which corresponds to the injection quantity.

FIG. 2 shows a functional block diagram of the closed-loop speed controlsystem. The input variable of the closed-loop speed control system is aset speed nM(SL). The output variable of the closed-loop speed controlsystem is the unfiltered actual speed nM(IST). A first filter 12 forcomputing the first actual speed nM1(IST) from the current unfilteredactual speed nM(IST) is provided in a first feedback path. The firstfilter 12 is usually designed as a two-revolution filter, i.e., itaverages the actual speed NM(IST) over one operating cycle correspondingto 720° of the crankshaft. A second filter 13 for computing a secondactual speed nM2(IST) from the current unfiltered actual speed nM(IST)is provided in a second feedback path. The second filter 13 is realized,e.g., as a mean value filter with a filter angle of a 90° crankshaftangle. The second filter 13 thus has significantly greater dynamics thanthe first filter 12.

A first control deviation dR1 is computed at a first comparison point A.It is determined from the set speed nM(SL) and the first actual speednM1(IST). The first control deviation dR1 is the input variable of thespeed controller 11. A second control deviation dR2 is computed at asecond comparison point B. It is determined from the set speed nM(SL)and the second actual speed nM2(IST). The second control deviation dR2is also supplied to the speed controller 11. The internal structure ofthe speed controller 11 will be explained in connection with thedescription of FIGS. 3 and 5. The speed controller 11 determines acorrecting variable from the input variables. In FIG. 2, this correctingvariable is designated as a power-determining signal ve. Thepower-determining signal ve represents the input variable for thecontrolled system, which in the present case is the internal combustionengine 2. The output variable of the controlled system corresponds tothe unfiltered actual speed nM(IST). The automatic control system isthus closed.

The invention is designed in such a way that during steady-stateoperation of the drive unit, the speed controller 11 computes thepower-determining signal ve exclusively as a function of the firstcontrol deviation dR1. When a dynamic change of state occurs, the speedcontroller 11 determines the power-determining signal ve as a functionof the first control deviation dR1 and the second control deviation dR2.

FIG. 3 shows a functional block diagram that represents a firstembodiment of the internal structure of the speed controller 11. Thespeed controller 11 comprises a proportional component (P component) 15for determining a proportional component ve(P) of the power-determiningsignal ve, an integral-action component (I component) 16 for determiningan integral-action component ve(I) of the power-determining signal ve, acharacteristic curve 14, and a summation unit 18. The first controldeviation dR1 is the input variable for the P component 15 and the Icomponent 16. The second control deviation dR2 is supplied to thecharacteristic curve 14. The output variable of the characteristic curve14 is a factor kp2, which acts on the P component 15. Another inputvariable of the P component 15 is a factor kp1. The characteristic curveis shown in FIG. 4. Values of the second control deviation dR2 areplotted in the positive/negative direction on the x-axis. The y-axisrepresents the factor kp2. A first limiting value GW1 and a secondlimiting value GW2 are plotted on the x-axis. At very large negativevalues of the second control deviation dR2, the factor kp2 is limited toa value GW3. A negative control deviation is present when the secondactual speed nM2(IST) is greater than the set speed nM(SL). At positivesecond control deviations dR2 that are greater than the second limitingvalue GW2, the factor kp2 is limited to the value GW4. In the regionbetween the first limiting value GW1 and the second limiting value GW2,the factor kp2 is set to the value zero. It is apparent from thecharacteristic curve 14 that in the steady state, i.e., where the secondcontrol deviation dR2 is almost zero, the factor kp2 has a value ofzero. Consequently, the P component 15 of the speed controller 11 isdetermined in this case exclusively from the first control deviationdR1. In the event of dynamic changes of state, i.e., where there is alarge negative or positive second control deviation dR2, the factor kp2acts on the P component 15 of the speed controller 11. The P componentof the power-determining signal is now computed as a function of thefirst control deviation dR1 and the factors kp1 and kp2:ve(P)=dR1·(kp1+kp2)where

-   ve(P)=proportional component of the power-determining signal ve-   dR1=first control deviation-   kp1=first factor-   kp2=second factor

The factor kp1 can either be preset as a constant or computed as afunction of the first actual speed nM1(IST) and/or the I componentve(I).

Another possibility for computing the P component ve(P) is to use thecontrol deviation dR2 directly for the computation of the P component15:ve(P)=dR1·kp1+dR2·kp2where

-   ve(P)=proportional component of the power-determining signal ve-   dR1=first control deviation-   dR2=second control deviation-   kp1=first factor-   kp2=second factor

This embodiment is shown by the dotted line in FIG. 3. The P componentand the I component are added in the summation unit 18. The sumcorresponds to the power-determining signal ve.

FIG. 5 shows a functional block diagram of a second embodiment of theinternal structure of the speed controller 11. In this embodiment, incontrast to the embodiment shown in FIG. 3, the second control deviationdR2 is supplied to the P component 15 and simultaneously to a DT1component 17. The DT1 component 17 computes the DT1 component ve(DT1) ofthe power-determining signal ve. The summation unit 18 then computes thepower-determining signal ve from the addends of the P component, Icomponent, and DT1 component. The DT1 component 17 is computed by acharacteristic curve 19, which is shown in FIG. 6. The time t is plottedon the x-axis. The y-axis corresponds to the DT1 component ve(DT1) ofthe power-determining signal ve. When there is a sudden change in thesecond control deviation dR2, it is assigned a corresponding valueve(DT1) by the characteristic curve 19. Two limiting values GW1 and GW2are plotted on the graph. The DT1 component is deactivated if the secondcontrol deviation dR2 becomes smaller than the first limiting value GW1,i.e., the signal ve(DT1) then has a value of zero. The DT1 component isactivated if the second control deviation dR2 becomes greater than thesecond limiting value GW2. The effect of the limiting value GW2 is that,when there are dynamic changes of state, i.e., when the second controldeviation dR2 has large positive or negative values, the DT1 componentis also incorporated in the computation of the power-determining signalve. When a steady state exists, i.e., where the second control deviationdR2 is practically zero, the power-determining signal ve is determinedexclusively from the P component and the I component.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A method for closed-loop speed control of an internal combustionengine, comprising the steps of: computing a first filtered actual speed(nM1(IST)) from an actual speed (nM(IST)) of the internal combustionengine by means of a first filter; computing a first control deviation(dR1) from a set speed (nM(SL)) of the internal combustion engine andthe first filtered actual speed (nM1(IST)); determining apower-determining signal (ve) for automatically controlling the speed ofthe internal combustion engine from the first control deviation (dR1) bymeans of a speed controller; computing a second filtered actual speed(nM2(IST)) from the actual speed (nM(IST)) of the internal combustionengine by means of a second filter; computing a second control deviation(dR2) from the set speed (nM(SL)) and the second filtered actual speed(nM2(IST)); and, when a dynamic change of state occurs, determining thepower-determining signal (ve) for the closed-loop speed control of theinternal combustion engine with the speed controller from the firstcontrol deviation (dR1) and the second control deviation (dR2).
 2. Themethod for the closed-loop speed control of an internal combustionengine in accordance with claim 1, wherein the second filter has asmaller filter angle than the first filter.
 3. The method for theclosed-loop speed control of an internal combustion engine in accordancewith claim 1, including detecting the dynamic change in state by way ofthe second control deviation (dR2).
 4. The method for the closed-loopspeed control of an internal combustion engine in accordance with claim3, wherein the second control deviation (dR2) acts on a DT1 component ofthe speed controller.
 5. The method for the closed-loop speed control ofan internal combustion engine in accordance with claim 4, includingdetermining the DT1 component from the second control deviation (dR2) byway of a characteristic curve.
 6. The method for the closed-loop speedcontrol of an internal combustion engine in accordance with claim 5,including deactivating the DT1 component by means of the characteristiccurve if the second control deviation (dR2) becomes smaller than a firstlimiting value (GW1) (dR2<GW1), and activating the DT1 component bymeans of the characteristic curve if the second control deviation (dR2)becomes greater than a second limiting value (GW2) (dR2>GW2).
 7. Themethod for the closed-loop speed control of an internal combustionengine in accordance with claim 3, wherein the second control deviation(dR2) acts on a P component of the speed controller.
 8. The method forthe closed-loop speed control of an internal combustion engine inaccordance with claim 7, including determining the P component from thefirst control deviation (dR1), a first factor (kp1), and a second factor(kp2), with the second factor (kp2) being computed from the secondcontrol deviation (dR2) by way of a characteristic curve.
 9. The methodfor the closed-loop speed control of an internal combustion engine inaccordance with claim 8, including additionally computing the Pcomponent from the second control deviation (dR2).
 10. The method forthe closed-loop speed control of an internal combustion engine inaccordance with claim 8, wherein the first factor (kp1) is either presetas a constant or computed as a function of the first filtered speed(nM1(IST)) and/or an I component (ve(I)).